1. Department of Virology, Nagoya University Graduate School of Medicine Tsurumai-cho 65, Showa-ku, Nagoya 466-8550, Japan
2. PRESTO, Japan Science and Technology Agency, Honcho 4-1-8, Kawaguchi, Saitama 332-0012, Japan
3. Department of Pathology, National Institute of Infectious Disease, Toyama 1-23-1, Shinjuku-ku, Tokyo 162-8640, Japan
4. Department of Pediatrics, Nagoya University Graduate School of Medicine Tsurumai-cho 65, Showa-ku, Nagoya 466-8550, Japan